Abstract:

Developing a highly efficient and low-priced iron-based oxygen carrier is the key to the application of chemical looping reforming of natural gas for hydrogen production. In order to explore the basic principle of designing such an oxygen carrier, the methane-pulsing reduction characteristics of Fe₂O₃-Al₂O₃ oxygen carriers with different Fe₂O₃ contents were studied at 800℃ and without the influence of external and internal diffusion by using a self-designed reactor system capable of on-line methane pulsing and synchronized analysis of gaseous reaction products. The results show that the reduction reaction of Fe₂O₃ proceeds according to a two-stage mechanism, which can stop at Fe₂O₃ or completely proceed to FeO with the content of Fe₂O₃ in the oxygen carrier particles. The variation pattern of the molar ratio of CO₂ to CO in the gas phase product with the number of CH₄ pulses is also closely related to the content of Fe₂O₃. Pulse reduction results of particles prepared from a mixture of α-Al₂O₃ powder and powdery 80% (mass) Fe₂O₃-Al₂O₃ oxygen carrier further reveal that the reduction degree of Fe₂O₃ in a single particle as well as in the whole bed is determined by the molar ratio of CH₄ entering the particle per unit time to the absolute amount of Fe₂O₃ in the particle. At last analysis on the correlations of the reduction degree of Fe₂O₃ and CH₄ conversion and CO₂ selectivity leads to a conclusion that only limiting the reduction process of Fe₂O₃ oxygen carries to the stage of Fe₃O₄ formation could yield a reacted stream of a sufficiently high CO₂ concentration for low-cost recovery of high purity CO₂.

Key words: methane, pulse reaction, chemical looping, hydrogen production, oxygen carrier, reactor

摘要：

开发高效廉价铁基载氧体是天然气化学链重整制氢技术走向应用的关键。为探究高效铁基载氧体设计的基本依据，利用自行设计的脉冲反应器和气体产物全量同步在线分析系统，在800℃和无内外扩散影响的条件下研究了不同Fe₂O₃质量分数的Fe₂O₃-Al₂O₃载氧体的甲烷脉冲法还原特性。结果表明：Fe₂O₃的还原反应依两段机理进行，随载氧体颗粒内Fe₂O₃含量的多少可停止于Fe₃O₄，也可完全进行至FeO；气相产物中CO₂与CO的摩尔比随CH₄脉冲次数的变化规律也与Fe₂O₃含量密切相关。对用α-Al₂O₃粉末稀释高Fe₂O₃质量分数载氧体粉末的方法制备的低Fe₂O₃质量分数颗粒进行的脉冲还原实验结果，进一步揭示单位时间进入单个载氧体颗粒内的CH₄量与其Fe₂O₃含量的摩尔比决定单个颗粒以及整个床层的Fe₂O₃还原度。最后对还原度和CH₄转化率以及CO₂选择性数据进行关联分析，发现只有将载氧体的还原过程止于生成Fe₃O₄阶段才能得到较高的CO₂选择性，从而达到低成本回收高纯CO₂的目的。

关键词: 甲烷, 脉冲, 化学链, 制氢, 载氧体, 反应器